Simulations of fatigue crack propagation in friction stir welds under flight loading conditions

Since Friction Stir Welding has been identified as a key technology for primary aerospace structures, fatigue crack growth testing and modelling is required. However, there is still a complete lack of information regarding the fatigue crack propagation in friction stir welds under variable amplitude loading and flight loading conditions. Experimental investigations have been performed on Centre cracked 4 mm thick AA2024-T3 base metal and FSW specimens: regarding the FSW samples, the crack was placed 5 mm out of the weld centre, in the most critical part of the joint: the coupons have been tested under simple variable amplitude load sequences, and under a standardized flight-simulation load history, Falstaff. The fatigue crack propagation was then predicted using widespread aerospace fracture mechanics software packages. Interaction effects and internal residual stresses were firstly separately simulated and than combined in order to evaluate the ability to predict the fatigue crack propagation on FSW welded structures under service loading conditions.